Test method for evaluating durability of carbon-plated coating of metal bipolar plate of fuel cell by using dynamic electrochemistry

Abstract

The invention discloses a test method for evaluating the durability of a carbon-plated coating of a metal bipolar plate of a fuel cell by using dynamic electrochemistry, which comprises the following steps: cutting the metal bipolar plate to be tested containing the carbon-plated coating into a sample with a predetermined size, and packaging the sample in an electrochemical corrosion test pool containing a corrosion solution; carrying out oxygen bubbling treatment on the etchant solution, and controlling the temperature of the etchant solution to the working temperature of the cathode of the fuel cell; the method comprises the following steps: testing the initial electrochemical performance of a sample by adopting a three-electrode system, carrying out constant potential action on a to-be-tested metal bipolar plate so as to accelerate the surface corrosion of the carbon-plated coating, testing a cyclic voltammetry curve at different time periods, and evaluating the durability of the carbon-plated coating of the metal bipolar plate of the fuel cell. According to the method, the corrosion resistance change of the carbon-plated coating under high potential is disassembled, analyzed and evaluated by a method of combining constant potential and cyclic voltammetry; the method can be used for testing the conductivity and morphology characteristics of the coating in different corrosion stages, is simple to operate, and does not need to adopt impedance and other high-requirement test equipment.

Description

Technical Field

[0001] The invention relates to the field of fuel cell material testing, and in particular to a testing method for evaluating the durability of a carbon-plated coating on a metal bipolar plate of a fuel cell using dynamic electrochemistry. Background Art

[0002] Proton exchange membrane fuel cells are green energy devices with high energy density and no pollution. As one of the most important core structural components in fuel cells, the corrosion resistance and surface conductivity of bipolar plates directly affect the overall performance and service life of the battery. Among bipolar plates, metal bipolar plates have advantages such as high volume / weight power ratio and low processing cost, but they also have problems such as insufficient corrosion resistance and poor surface conductivity.

[0003] Metal coating is an effective means to improve the conductivity and corrosion resistance of the metal bipolar plate surface, mainly including carbon-based coating, metal-based coating and conductive polymer coating; carbon-based coating has excellent corrosion resistance, and excellent electrical and thermal conductivity, and has been widely studied, mainly divided into pure carbon film, transition metal carbide, carbon / ceramic composite coating, etc.

[0004] During the actual operation of the fuel cell, the carbon-plated coating will undergo significant changes in the surface morphology of the plate due to high temperature, high humidity, and the presence of oxygen. The main reason is that the bonding force of the carbon coating is weakened due to the precipitation of the transition layer metal, and the carbon functional layer falls off. In addition, the transition layer metal easily forms a metal oxide passivation film under oxygen conditions. The passivation film has a certain anti-corrosion ability, but its contact resistance is large, and in the subsequent process, the passivation film will dissolve until the stainless steel substrate is precipitated. Therefore, for the carbon-plated coating, its coating failure generally includes the shedding of the carbon functional layer and the formation and decomposition process of the metal oxide passivation film.

[0005] The existing durability evaluation method of carbon-plated coating generally adopts constant potential effect to evaluate the corrosion resistance of the coating by the change of corrosion current. However, due to the problem of passive film formation, during the constant current test, the corrosion current usually drops rapidly first, then increases, and finally drops. This method cannot well analyze the process of complete shedding of the carbon coating and the formation of the passivation film.

[0006] And the patent application with publication number CN114136878A discloses a method for testing the corrosion resistance of a metal bipolar plate coating of a fuel cell, which method includes the following steps: in an electrochemical test device of a three-electrode system, an impedance test is performed on the metal bipolar plate coating to obtain a Nyquist diagram; based on the Nyquist diagram, an equivalent circuit simulation of the metal bipolar plate coating is performed to determine the values ​​of each component in the circuit; the charge transfer impedance Rct value obtained when the metal bipolar plate coating covers the substrate intact is calibrated as a reference value; after the bipolar plate is used, an impedance test is performed again, and the charge transfer impedance Rct is compared with the reference value to evaluate the corrosion resistance of the metal bipolar plate coating. However, this invention requires the use of high-requirement test equipment such as impedance. Summary of the invention

[0007] Based on the deficiencies in the prior art, the present invention provides a test method for evaluating the durability of a carbon coating on a metal bipolar plate of a fuel cell using dynamic electrochemistry.

[0008] Cyclic voltammetry is an important test method for testing the electrochemical properties of materials. Different materials and different morphologies of the same material will present different curves in the cyclic voltammetry test. For carbon-plated coatings, since their functional layer is amorphous carbon, the density of their surface coating will directly affect the double-layer test effect. The present invention intends to utilize this characteristic of amorphous carbon to provide a test method for evaluating the corrosion behavior of carbon-plated stainless steel plates using dynamic electrochemistry. By combining constant potential with cyclic voltammetry, the corrosion resistance changes of carbon-plated coatings at high potentials are analyzed and evaluated.

[0009] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0010] The present invention provides a test method for evaluating the durability of a carbon coating on a metal bipolar plate of a fuel cell using dynamic electrochemistry, comprising the following steps:

[0011] (1) encapsulating the metal bipolar plate to be tested containing the carbon coating in an electrochemical corrosion test cell and adding a corrosion solution;

[0012] (2) subjecting the corrosion solution to oxygen bubbling treatment and controlling the temperature of the corrosion solution to the operating temperature of the fuel cell cathode;

[0013] (3) Using a three-electrode system to test the initial electrochemical performance of the metal bipolar plate to be tested;

[0014] (4) subjecting the metal bipolar plate to be tested to a constant potential to accelerate the surface corrosion of the carbon coating, and testing the cyclic voltammetry curve of the metal bipolar plate to be tested at different time periods, and evaluating the durability of the carbon coating on the metal bipolar plate of the fuel cell in combination with the initial electrochemical performance tested in step (3).

[0015] The purpose of testing the initial electrochemical performance is to compare it with the cyclic voltammetry curve data of the metal bipolar plate to be tested in step (4) to evaluate its corrosion resistance.

[0016] As a preferred solution, in step (1), the metal bipolar plate to be tested containing the carbon coating is cut into samples of a predetermined size, wherein the predetermined size is 2.5 cm×2.5 cm. The corrosion solution is H 2 SO 4 The aqueous solution contains NaF at a mass concentration of 0.01-5ppm. NaF is highly corrosive to the carbon coating and can accelerate the corrosion of the carbon coating.

[0017] Preferably, in step (1), the contact area between the sample and the corrosive solution is a circle with a diameter of 1 cm.

[0018] Specifically, in step (1), the carbon coating includes but is not limited to a pure carbon film, a transition metal carbide coating, a carbon / ceramic composite coating, a carbon-based alloy, a conductive polymer or a diamond-like film.

[0019] Preferably, in step (2), the oxygen bubbling time is 30-90 minutes, and the temperature of the corrosion solution is controlled to 60-90° C. by circulating water to simulate the working environment of the fuel cell cathode.

[0020] Preferably, in step (3), the three-electrode system comprises: a working electrode formed by the sample, a counter electrode formed by a platinum mesh, and an Ag / AgCl reference electrode.

[0021] Preferably, in step (3), the working voltage of the constant potential effect is 1.1-1.4 V vs Ag / AgCl, and the constant potential effect is performed on the same electrode plate for 2-10 hours.

[0022] Preferably, the testing method further comprises observing the surface morphology of the coating through a high-power microscope after the constant potential action.

[0023] The evaluation of the durability of the carbon-plated coating on the metal bipolar plate of the fuel cell includes analyzing the corrosion resistance and corrosion mechanism of the carbon-plated coating based on changes in the cyclic voltammetry curve and the surface morphology of the coating observed under a high-power microscope.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention uses a method combining constant potential and cyclic voltammetry to disassemble, analyze and evaluate the changes in the corrosion resistance of the carbon-plated coating under high potential, and judges the corrosion resistance of the coating by the density of the coating structure; this method can test the conductivity and morphology characteristics of the coating at different corrosion stages, is simple to operate, and can be completed by a conventional electrochemical workstation without the need to use high-requirement testing equipment such as impedance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The constant potential action curves of Example 1 at different times; A is the constant potential action curve within 60 min; B is the constant potential action curve of 75-100 min.

[0027] Figure 2 The cyclic voltammetry curves after constant potential action at different times in Example 1; A is the cyclic voltammetry curve within 60 min; B is the cyclic voltammetry curve from 75 to 100 min.

[0028] Figure 3 These are the constant potential action curves of Example 2 at different times; A is the constant potential action curve within 45 min; B is the constant potential action curve from 45 to 105 min.

[0029] Figure 4 The cyclic voltammetry curves after constant potential action at different times in Example 2; A is the cyclic voltammetry curve within 45 min; B is the cyclic voltammetry curve from 45 to 105 min.

[0030] Figure 5 The surface morphologies of Example 1 (A) and Example 2 (B) after constant potential action. DETAILED DESCRIPTION

[0031] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0032] Example 1

[0033] The metal bipolar plate sample 1 to be tested containing a carbon coating (purchased from Shanghai Jie Hydrogen Technology Co., Ltd.) was cut into 2.5 cm*2.5 cm samples, washed with deionized water and placed in an air oven to dry at 90°C for 1 hour; the sample was then packaged in an electrochemical corrosion cell (commercially purchased), filled with a prepared pH=1 sulfuric acid aqueous corrosion solution containing 1 ppm NaF, and the sample coating was completely immersed, that is, the area of ​​a circle with a diameter of 1 cm was exposed to contact with the corrosion solution to ensure that the corrosion area of ​​each plate was consistent; the corrosion solution was bubbled with oxygen for 30 minutes, and then heated by circulating water in a high-temperature water bath to maintain the corrosion solution at 80°C to simulate the working environment of the cathode of the plate; then a three-electrode system (a working electrode composed of sample 1, a counter electrode composed of a platinum mesh, and an Ag / AgCl reference electrode) was used to perform an electrochemical test on the sample, firstly performing a 30-min open circuit test to remove impurities on the surface of the coating; then the coating was subjected to a constant potential durability test, with the voltage set to 1.4V vs Ag / AgCl, test its cyclic voltammetry curve at regular intervals, and then continue the constant potential test. The total constant potential test time is 6 hours. After the test, remove the coated plate, rinse it with distilled water, place it in an air drying oven at 80℃ for 0.5h, and observe the morphology changes.

[0034] Example 2

[0035] The metal bipolar plate sample 2 (State Power Investment Group Hydrogen Energy Technology Development Co., Ltd.) to be tested containing a carbon coating was cut into 2.5 cm*2.5 cm samples, washed with deionized water and then placed in an air oven and dried at 90°C for 1 hour; the sample was then encapsulated in an electrochemical corrosion cell, filled with a prepared sulfuric acid aqueous corrosion solution with a pH of 1 and containing 1 ppm NaF, and the sample coating was completely immersed, that is, the area of ​​a circle with a diameter of 1 cm was exposed to contact with the corrosion solution to ensure that the corrosion area of ​​each plate was consistent; the corrosion solution was bubbled with oxygen for 30 minutes, and then heated by circulating water in a high-temperature water bath to maintain the corrosion solution at 80°C to simulate the working environment of the cathode of the plate; the sample was then electrochemically tested using a three-electrode system, firstly subjected to a 30-min open circuit test to remove impurities on the surface of the coating; the coating was then subjected to a constant potential durability test, with the voltage set to 1.4 V vsAg / AgCl, and its cyclic voltammetry curve was tested at regular intervals, and then the constant potential test was continued, with a total constant potential test time of 6 hours. After the test, the coated plates were removed, rinsed with distilled water, and placed in an air drying oven at 80°C for 0.5 h to observe the morphological changes.

[0036] Depend on Figure 1It can be seen that under the action of high potential, the amorphous carbon coating of the carbon-plated coating in Example 1 is continuously peeled off, causing the corrosion current to continuously rise after decreasing. The two obvious corrosion current increase values ​​at around 28min and 50min are presumed to be the corrosion and shedding of carbon in the outermost amorphous coating and the inner titanium-carbon coating and the continuous formation of titanium metal oxide. During the time of 55-120min, the titanium metal oxide maintains a stable state and the corrosion current does not change.

[0037] Depend on Figure 2 It can be seen that after the coating has been corroded at high potential for different time periods, its cyclic voltammetry curve changes significantly; Figure 2 In B, after 15 minutes of action, the double electric layer of its CV curve becomes larger, indicating that after the high potential action, the density of the carbon coating changes significantly, the pores between the particles become larger, and the carbon film is falling off; in the stage of 30-60 minutes, the CV curve is also gradually increasing, but the rate of change is not fast, which is consistent with the trend of the constant potential action curve; and in the stage of 75-120 minutes, Figure 2 In B, the CV curves almost overlap, which indicates that at this stage, the coating surface is already in a steady state; through the above experiments, we speculate that the carbon coating has almost completely fallen off at 50 minutes, and then a titanium oxide passivation film continues to form on the coating surface until a new steady state is reached. The oxide passivation film can exist stably until 120 minutes.

[0038] Depend on Figure 3 From the corrosion current test, it can be seen that the corrosion current of the carbon-plated coating in Example 2 increased significantly at around 33 minutes, and this stage was the drastic shedding of the carbon-plated coating; then the corrosion current continued to decrease until 110 minutes when the corrosion current increased significantly, and then tended to a relatively stable state; based on this experimental phenomenon, it is speculated that the interval from 33 minutes to 110 minutes is the corrosion decomposition stage of the niobium metal transition layer until the stainless steel substrate is exposed. After the oxide passivation film is formed, it rises instantly after 110 minutes and then remains stable.

[0039] exist Figure 4 We found that the maximum double electric layer of Example 2 appeared at 30 min, which is consistent with the obvious increase in the constant potential test at 33 min, indicating that Example 2 maintains the carbon coating at a high potential for 33 min; unlike Example 1, its cyclic voltammetry curve continuously decreases in the range of 30-120 min, which indicates that the metal oxide of the transition layer is continuously decomposing, resulting in a significant change in the density of the passivation film.

[0040] Attached Figure 5In the embodiment 1, after the constant potential is applied, the surface carbon coating is obviously peeled off, exposing the yellow metal passivation layer, and the metal passivation is partially peeled off; while in the embodiment 2, after the constant potential is applied, the color of the corrosion area is white, which is presumed to be the stainless steel substrate exposed after the metal oxide passivation film is decomposed, indicating that different coatings present different surface morphologies after the constant potential is applied;

[0041] Through the tests of Example 1 and Example 2, it is proved that the dynamic electrochemical method provided by the present invention can accurately evaluate the corrosion state of the carbon-plated coating at different stages under high potential, and the difference in the elements of the metal transition layer will lead to differences in the stability and corrosion resistance of the carbon coating and the metal oxide passivation film; the method of the present invention can well evaluate and disassemble the failure process of different carbon coatings under high potential.

Claims

1. A test method for evaluating the durability of a carbon coating on a metal bipolar plate of a fuel cell using dynamic electrochemistry, characterized in that: The following steps are involved: (1) encapsulating the metal bipolar plate to be tested containing the carbon coating in an electrochemical corrosion test cell and adding a corrosion solution; (2) subjecting the corrosion solution to oxygen bubbling treatment and controlling the temperature of the corrosion solution to the operating temperature of the fuel cell cathode; (3) Using a three-electrode system to test the initial electrochemical performance of the metal bipolar plate to be tested; (4) subjecting the metal bipolar plate to be tested to a constant potential to accelerate the surface corrosion of the carbon coating, and testing the cyclic voltammetry curve of the metal bipolar plate to be tested at different time periods, and evaluating the durability of the carbon coating on the metal bipolar plate of the fuel cell in combination with the initial electrochemical performance tested in step (3).

2. The testing method according to claim 1, characterized in that: In step (1), the metal bipolar plate to be tested containing the carbon coating is cut into samples of a predetermined size, wherein the predetermined size is 2 to 4 cm×2 to 4 cm.

3. The testing method according to claim 2, characterized in that: In step (1), the contact area between the sample and the corrosive solution is a circle with a diameter of 1 cm.

4. The testing method according to claim 1, characterized in that: In step (1), the corrosion solution is an aqueous H2SO4 solution with a pH value of 1-5, wherein the mass concentration of NaF contained therein is 0.01-5 ppm.

5. The testing method according to claim 1, characterized in that: In step (1), the carbon coating is a pure carbon film, a transition metal carbide coating, a carbon / ceramic composite coating, a carbon-based alloy, a conductive polymer or a diamond-like film.

6. The testing method according to claim 1, characterized in that: In step (2), the oxygen bubbling time is 30-90 minutes, and the temperature of the corrosion solution is controlled to be 60-90° C. by circulating water.

7. The testing method according to claim 1, characterized in that: In step (3), the three-electrode system includes: a working electrode composed of the sample, a counter electrode composed of a platinum mesh, and an Ag / AgCl reference electrode.

8. The testing method according to claim 1, characterized in that: In step (3), the working voltage of the constant potential effect is 1.1-1.4V vsAg / AgCl, and the constant potential effect is performed on the same electrode plate for 2-10 hours.

9. The testing method according to claim 1, characterized in that: The test method also includes observing the surface morphology of the coating through a high-power microscope after the constant potential action.

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